text:
Are there any safety data on the aircraft used for skydiving?
I am planning a (first) skydive, a tandem jump with an instructor. However, I have not picked which school I will use yet.
I am convinced about the safety of the jump itself, but cannot find reliable data on accidents that have occurred during the actual flight.
How safe are aircraft that are used for skydives? What are the statistics compared to commercial aviation?

Why worry about the safety of the aircraft used? You are already wearing a parachute when on board ;-)

@MadMarky If there is a takeoff incident, I don't think that will help :)

As a former jumper and a former motorcylist, I consider the motorcycle activity quite a bit more dangerous than the skydiving activity.

@Cloud, you are in the UK?

What aircraft are used at the schools you are considering?

@CrossRoads Why do some of the flight status say unknown? https://www.flightradar24.com/data/aircraft/g-sylv

"I have not picked which school I will use yet." doesn't quite add up with "I am visiting friends for the jump, which is in the UK. The aircraft has this on the side of it: G-SYLV" How can you know which exact aircraft you'll be jumping from if you haven't picked an operator?

I don't know.  They have the flight track.  Looks like a Grand Caravan (C208), which was discussed as being more reliable.

@MichaelKjörling It is one of the operators we are considering / likely to use at this stage, pending my research and analysis on safety.

I'm an ex jumper and I'd say the two major risks in a skydiving airplane ride are engine failure on take off or while too low to bail out, and a canopy deployment out an open door while in flight.
If you're in a piston engine Cessna 206 and the engine quits at 200 feet and there isn't lots of runway still out front, it's gonna hurt.  If you're in a piston twin like a Seneca and an engine quits and you're heavily loaded, usually the good engine succeeds only in taking you directly to the scene of the crash (piston twins at gross weight are so marginal that it's safer to treat them as a single engine with a really flat glide).
Single engine turbine like a Caravan, much better because the engine is way more reliable than something like a 6 cylinder IO-540. If it's a turbine twin machine like a King Air or Twin Otter, with turbine reliability and the single engine performance is adequate, this would be the safest.
Really though, the same applies to any airplane ride, but in a jump plane you're more exposed by not being strapped into a seat.
The other risk, canopy deployments, is mitigated by having a jump door and the deployment risk is only in the couple minutes at altitude where you're in the open door.  If no jump door, it takes intense vigilance by the jump master to prevent someone's pilot chute from coming loose on the entire ride up.
So if I had to choose between a skydiving center where I have to ride up in a single engine piston like a 206, or one that used a Caravan, I'd go with the Caravan.  And if another one used a Twin Otter, I'd go with that one.  All other factors being equal of course.  And I wouldn't go in one without a jump door (although I doubt anybody flies with without them these days).

Thank for this great answer. If there is a deployment whilst inside the aircraft though, what is the problem? Why not just abort the jump? I found the aircraft now and it is a Cessna 208B Grand Caravan

Because if a pilot chute comes out of its pouch or a reserve pilot chute pops out, and the door is open, it will end up in the airstream and you will now enjoy a canopy extraction and deployment out the door, which may or may not get caught up in the tail, causing ever more enjoyable levels of excitement.  This is why jump pilots often wear emergency parachutes.   As I said on your other post, you are thinking way too hard about all this.  Unless the skydive centre itself has a bad accident record, stop worrying about that stuff and have a good time.

You didn't mention any particular country, but for the US I found an NTSB report called On the Safety of Parachute Jump Operations. It's from 2008 so some of it may be dated, but it says that no reliable data exist (emphasis mine):

According to USPA safety records, from 1992 through 2007, about 30
  parachutists per year were killed in jumping mishaps. Safety Board
  accident data show that, for the same time frame, about five
  parachutist fatalities per year resulted from accidents involving
  parachute operations aircraft. Direct comparisons of associated risk
  are difficult to calculate due to the likelihood of multiple
  parachutists being carried on each flight and a lack of departure data
  for parachute jump operations. The Safety Board notes that the FAA
  does not have data on the number of parachute jump operators or the
  number and type of aircraft used in parachute jump operations in the
  U.S. The absence of these data precludes any calculations of safety
  statistics for parachute jump operations, including accidents rates.

Based on that information, you have 5 fatalities per year related to aircraft, and 25 that are not. So the aircraft should be the least of your worries.
Here are some key points from the rest of the report:

a segment of U.S. general aviation operations, which, according to
  data compiled by the United States Parachute Association
  (USPA),[1]transports parachutists on 2.16 to 3 million jumps
  annually.[2]
[...]
Since 1980, 32 accidents involving parachute operations aircraft have
  killed 172 people; [6]most of whom were parachutists.
[...]
The investigation identified maintenance discrepancies on the airplane
  and deficiencies with the pilot's performance of emergency procedures;
  these issues prompted the Safety Board to examine accident reports for
  parachute operations to determine if such safety issues may be
  widespread. The results, discussed in this investigation report, show
  that these issues were present in many accidents
[...]
The Safety Board's review of parachute operations accidents since 1980
  identified the following recurring safety issues:

Inadequate aircraft inspection and maintenance;
Pilot performance deficiencies in basic airmanship tasks, such as preflight inspections, weight and balance calculations, and emergency
  and recovery procedures; and
Inadequate FAA oversight and direct surveillance of parachute operations.

Anecdotally, skydiving is indeed associated with poor maintenance and hiring low-time commercial pilots. It's one of the few commercial activities that doesn't require an air operator certificate (see 14 CFR 119.1(e)(6)) so it can operate under part 91, without the more stringent rules and requirements of part 135. That also means there are no minimum hours required for the pilot as long as he holds a commercial certificate, and it's a very sought-after job for commercial pilots who want to build hours without instructing.
However, anecdotes tell you nothing useful at all about the overall safety of the industry, or about the safety of an individual skydiving operation. Some research is good and I think you can look for some common sense things that you might look for in any business: professional location, good customer service, good online presence, good reviews etc. But trying to quantify the risk in a meaningful way is extremely difficult, and you still have to balance it against the reward and against the risks of whatever else you would do that day instead of skydiving.

I think the way you ask the question is wrong and the comments are here on spot. However, I get your concerns; after all it would be better to die due to a malfunctioning parachute rather than a plane crash, right?
To answer your question first we need to know the type of aircraft. I will take two examples here. (if you need any other type you can check it on aviation-safety.net)
Stats for Cessna 208 Caravan:
Hull-losses:    222
Hull-loss accidents:    211 with a total of 446 fatalities
Criminal occurrences (hull-losses, excl. hijackings):   0   with a total of 0 fatalities
Hijackings: 6   with a total of 1 fatalities
Survival rate:  28.8%   of all occupants survived fatal accidents

Stats for Beechcraft King Air:
Hull-losses:    218
Hull-loss accidents:    188 with a total of 503 fatalities
Criminal occurrences (hull-losses, excl. hijackings):   5   with a total of 2 fatalities
Hijackings: 1   with a total of 0 fatalities
Survival rate:  8.7%    of all occupants survived fatal accidents

"Afterall it would be better to die due to a malfunctioning parachute rather than a plane crash,right?" Why would it be? In both cases, there's very little you can do to increase your odds of survival after the bad thing happens. In both cases, you would typically have time to contemplate your fate between the moment when it's obvious that things are going horribly wrong, and your impact with the ground. Seems about the same to me either way.

Maybe i should have added a smiley like that :) in the end of that sentence. It was a sarcasm, since op wanted to skydive but concerns about plane safety when there is so many aspects that might go wrong.

You guessed right. It is a 208 Caravan I use: https://www.flightradar24.com/data/aircraft/g-sylv


text:
What does it mean to "lock on" to a DME ground station?
I was just reading about the working of the DME the other day and then I read a para which said:

The aircraft interrogator "locks on" to the DME ground station once it
  recognizes a particular pulse sequence having the same spacing as the
  original interrogation sequence

Can anybody please elaborate on the above statement? I just want to know what is "lock on" and how does an aircraft interrogator lock on to a DME ground station?

Possible duplicate: How does an airborne DME unit differentiate itself?

"Lock-on" just refers to a unit receiving multiple different response signals in response to its interrogation broadcasts, scanning for the signal it's looking for, and when it finds the signal who's encoding matches its channel selection, it starts to process that signal and ignores all others.  It's locked on to that signal.

The ground station transmits responses to interrogations
from other aircraft and randomly timed signals that look
just like responses, so an aircraft has to pick responses to
its transmissions out of all the other signals that look
like they could be. The way it's done is by looking at the
ground station transmissions for a while trying to find a
time after its interrogations where there's usually a
response. (Not all interrogations get responses.) Once the
time slot is found the aircraft can calculate the distance
to the ground station and only has to track the changes in
the distance from then on. It reduces its interrogation rate in
accordance with its lighter workload and is locked on.

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text:
Could ejector seats save lives in commercial aircraft?
If cost were no issue (it could be done cheaply), would installing ejection seats for passengers possibly save lives?
There are certain scenarios (albeit extremely rare ones), where the crew may know with high probability that everyone on the aircraft is doomed. This might be because both pilots have been incapacitated or died, or the horizontal stabalizer has failed and the aircraft is in a nose-dive, something like that. In this case, the crew could automatically deploy everyone's ejection seats - this could increase the chances of survival.
Of course, one issue is the control of the parachute upon deployment, so I would suggest that some device knocks the passenger unconscious as they are ejected (like a knock to the head - to stop them tampering with anything) and then sensor waits for enough airspace to auto-deploy the chute.
Is this viable?
Edit: This is not a duplicate. The other question asks about parachutes on commercial aircraft but not ejection seats.

So to address an extremely rare circumstance, you're suggesting to put explosives under every passenger seat and devices to give them concussions?

first thought: what would be the mass budget for such a modification? Second thought: you may find many piece of answer by searching parachute and commercial aviation on this website

I don't agree it's a duplicate, the other question is asking about whole airplane chutes, not ejection seats.

"both pilots have been incapacitated or died" Please cite at least, or rather just, three examples of commercial flights where this has happened. Heck, please cite three examples of any kind of flight with more than one pilot up front where this has happened.

"If cost were no issue".... Very Funny.   In Aviation, cost is always an issue.

@MichaelKjörling Helios flight is one that comes to mind Also, previous events don't predict future ones. That's one from Money SE, i.e. investing.

like a knock to the head - to stop them tampering with anything - this doesnt work like in the movies! A knock on the head enough to render you unconscious usually mean you've just gotten enough brain damage to hinder your life. The payouts alone would make this worthless. It's like saying "Ignoring all impracticality" - if you ignore all the impracticality it becomes impracticable by definition!

Usual issue: such equipment is heavy.  That means fewer pax per flight.  That means more flights required for the same pax.  That means more unsurvivable accidents.   The ejector seats would therefore kill more people than if not fitted, even if technically/biomechanically feasible which, as others have explained is sensibly not.

Realistically no, the answer is similar logic to this question. If we overlook the weight and size toll there are still lots of practical issues.

Military jets generally have no (or limited) upper obstructions above the pilot aside from the canopy which is fairly easy to jettison. In a commercial aircraft you have oxygen masks, over head entertainment systems, then the overhead baggage compartment, then all the piping in the upper section of the plane to get rid of. This is assuming you want to use existing vertical exiting ejection seats. Shooting seats out of the side of plane creates a whole new slew of problems (into running engines, into the tail etc).
You need to be strapped into an ejection seat while wearing a harness so either everyone has to come suited up in a proper harness or you have to provide them. it would take quite a long time to board a full commercial airliner and strap everyone in.
Everyone would have to wear oxygen masks at all times. You can't go launching people out of a plane without supplemental oxygen. Since an emergency can occur at any time to be a viable solution everyone would have to sit there huffing on O2.
Ejection from an aircraft is very physically demanding on the body and even fighter pilots in top physical shape still can suffer severe injuries and may never fly again. You would be hard pressed to subject many average people to this successfully.
You now have hundreds of parachutes to check and re-pack all the time to make sure the seats are in good order.
On most commercial aircraft there is often bags stored on the floor, stuff in peoples laps etc. If seats start shooting out of the airframe all that debris is going with it and is quite liable to injure someone
And finally, who gets to pull the handle, who gets to decide everyone on the plane is about to go for quite the ride?

No, it's not viable:

Using ejection seats requires a certain level of physical fitness, you need strong bones, children and older people would get seriously injured or die using seats. Healthy people in the prime of their life still get injured or killed using seats
Using ejection seats requires recurrent training in getting the right posture before the seat is used, if someone using a seat is not in the right position the g forces will give them serious injuries. Just getting people strapped in requires skills, usually this is done with assistance from ground crew. If the occupant is not in the right position they will lose limbs from contact with the airplane as they are ejected from it. They also need training on how to land with a chute and what to do if they land in water, etc. Keep in mind the word recurrent here, so that's training for millions of people, over and over. Try teaching a 3 year old how to sit in an ejection seat, getting them to sit period is nearly impossible!
Most of the time passengers would not be in position to be ejected, they're walking around, they've got bags out, using laptops/tablets, eating with tray tables down, in order to be successfully ejected bags would have to be cleared (no place to put them though, there's no overhead bins as the seats have to go up), food trays cleared, people seated and strapped securely. It would take minutes to do this
Most aviation accidents are sudden, with not enough warning to make ejection seats useful. There are very few where there's enough warning that an escape system would help. Also, you'd have to have several seconds for that many people to eject, you couldn't punch them all out simultaneously as they'd get tangled up
Ejection wouldn't necessarily put people into a more survivable position. If you eject 300 people into the middle of the North Atlantic they will be dead in minutes from exposure

So in order to do any good you'd have to have enough warning and the airplane would have to be in the fortunate position to be in search and rescue range of a facility that can save an airplane full of people before they drown or die of the injuries sustained in the process. That's a tough sell.
Note: I'm assuming that the seat design itself would compensate for the lack of protective clothing, helmets, etc, and would also supply oxygen for high altitude ejections. If not, passengers would need to be wearing flight suits, helmets, etc.

-3 votes on the question, but +6 for the answer :/

I can't speak for the downvotes @Cloud, maybe a chat opportunity if you want wider views.

@Cloud As I said in response to a similar comment of yours on another question, answers can be good, or useful in answering the question, even if the question is poor.

Ejector seats are effectively explosives.
(what, you thought they were launched by rubberbands?)
You want to put explosives in every row of the cabin?
The same cabin where cell phone batteries sometimes catch fire, passengers spill drinks and throw up, and all equipment is kicked, pushed, knocked, and abused?
And you want those ejector seats to be completely safe so they never go off by accident or during a fire, but are also completely reliable so they always go off when needed.
Ejector seats throughout the cabin would turn even a "routine" galley-fire into a mass casualty mid-air explosion.

I once entered an Aermacchi and its ejection was by rubberbands =)

Since when are fires routine?

TL;DR: Nope!
This page goes into great detail about why ejection seats for airliners are a very ungood idea, so we'll just sit back and let them do the talking:

Pro: Safe recovery of passengers in the event of a catastrophic disaster.
Con:

Danger to maintainance crews
Danger to passengers due to accidental discharge
Possible injuries to passengers due to use
Weight increase
Larger seat area requires fewer seats in given area
Egress hatch requirement requires considerable redesign of cabin fuselage
Cost- Ejectable seat would add costs for:
a. Redesign costs
b. Development costs
c. Seats (military seats can cost upward of $100,000 per unit)
d. Periodic maintainance
e. Replacement parts
f. Maintainance crew training/explosive certification
Minimal time of use

[...]
...Parachutes require more than just a simple lap belt. At a minimum, the harness requirements include a pair of leg straps, a pair of shoulder straps and a chest strap. These straps must be adjusted for each individual to be a snug (read uncomfortable) fit for each passenger...  In the case of a situation requiring a mass ejection, this would have to be delayed until ALL passengers AND crew are strapped in securely prior to depressurizing the cabin, blowing the hatches and initiating ejection.
When the cabin is depressurized and the hatches are jettisoned, the passengers would be exposed to the lower oxygen pressure in the upper atmostphere, the wind blast which would cause flail injuries and injuries by loose flying objects such as handbags, cameras, camcorders, trays, carry-on bags, and other objects.
Jettisoning a large number of hatches in the roof of an airliner will also cause significant changes in the aerodynamics of the aircraft leading to control problems for the flight crew.
The aircraft structure would require massive modification to make ejection seats feasable, including strengthing the cabin floor for the additional weight and the recoil of the seat firings. The cabin roof would have to be configured with the aforementioned hatches. The fuselage would therefore need a major increase in supports to allow it to hold its shape when the hatches were jettisoned. Overhead baggage compartments, and underseat storage would have to be eliminated to give adequite clearance above and, because of the seat depth, below. Legroom would have to be adjusted to make sure that adequite clearance was maintained on ejection to prevent leg injuries.
Mechanical ejection (spring/bungie) would provide inadequite thrust to ensure that passengers would clear the empennage. Compressed gas systems that would have enough force would provide too great of an initial force for safety. This means that pyrotechnic rocket/catapult systems be used. These systems would necessitate significantly increased training for maintainance personel, cabin and flight crews. The pyrotechnics would require maintainance on a regular basis in an explosive rated hanger with explosive rated storage.
The ejection sequence would have to be from the rear to the front of the cabin, with the flight crew being the last of all to be ejected. In an airliner with 30 rows of seats, the seats would have to be jettisoned in row sets, with seperation rockets to insure dispersal of the seats and prevent mid-air seat collisions. There would have to be a delay between rows for the same reason. This delay in military jets is in the vicinity of .4 to .5 second. This adds up to some 15-16 seconds for a full ejection of the aircraft. Seats that are unoccupied must be weighted to ensure that they seperate in a predictable path. While the seats are firing, the aircraft would be exposed to forces from the catapult charges, and the center of gravity would be changing rapidly. This would cause significant difficulty to the flight control system to maintain stability.
[...]
Conclusion:
Passenger survival by seperating the passengers from the aircraft prior to impact is not an option that could be easily or cost effectivly implemented.

"leading to control problems for the flight crew" In fairness, OP already postulated an incapacitated or dead flight crew, so this should be less of a problem in practice in the OP's scenario. Still, it's definitely valid for the general case.

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text:
Can you be paid to taxi an aircraft if you don't have a commercial license?
From a strictly legal standpoint, in the US (I'm also interested in Canada) can you (not should you) accept compensation to taxi an aircraft if you don't have a commercial pilot's license? If I was a mechanic with just a private license, could I charge for my time while taxiing an aircraft?

I know there are mechanics who are "taxi qualified"(no pilot certificate required from what I've heard) at airlines, and are allowed to taxi the aircraft, usually from gate to a hangar or run-up pad. How this works reg wise I don't know, so I won't submit this as an answer.

I have a feeling that there is an implied for the purposes of air navigation somewhere in the regs, but I don't know where and don't have time to look it up right now.

likewise, we have several mechanics who are authorized to run up engines.  typically, though, our aircraft are pulled around by a tug, though this would entirely depend on the geography of your airfield.

The question -- title and content-- are about the legality of charging taxiing time when not holding having a commercial pilot's license, The current answers, including the selected one, discuss the legality of taxiing a plane. The question doesn't seem to be answered.

I would say yes you can as per the FAR as I read them the limitations on a PPL are

§61.113 (a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft

So you cant act as Pilot In Command for hire or if there are passengers on board (which in this case I assume there are not) however if we look at the FAR for the official definition of "Pilot In Command" we will find

Pilot in command means the person who:
(1) Has final authority and responsibility for the operation and safety of the flight;
(2) Has been designated as pilot in command before or during the flight; and
(3) Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight.

The question is does taxing count as a "Flight". I would think it does not and moving the aircraft around is part of maintenance (thats how they log the hours on the trainer planes I rent). The FAR definitions section (§1.1) does not seem to contain one for "flight" so that may be open to interpretation. But as I read it you can taxi the aircraft for compensation as its not a "Flight" and thus you are not the Pilot In Command which is when the PPL rules would come into play in my opinion.
However section §65.81 states

However, he may not supervise the maintenance, preventive maintenance, or alteration of, or approve and return to service, any aircraft or appliance, or part thereof, for which he is rated unless he has satisfactorily performed the work concerned at an earlier date.

The key line (Bolded) is return to service. If Taxing counts as returned to service then (unless rated to do so) you may not be able to for this reason (nothing to do with compensation).
Note: I am not a lawyer nor an aircraft mechanic and can not guarantee that my assumptions are correct. The opinions stated above should not be used as official legal advice and there may be more information in the FAR that I have not come across. This was compiled after some quick reading and searching in the assumed correct places.
Note 2: I would assume that in a commercial setting (and really any setting) there are some insurance implications to this kind of operation (especially with large aircraft). This may almost be a bigger concern than the legality of it (although both are important). You would not want to get into the situation where you may be legally allowed to drive the plane on the tarmac but are not covered by the company's insurance. Should you get into an accident you or your shop may become liable for the damages.

One interesting (probably relevant) definition in the FARs (14 CFR 1.1): "Flight time means:  Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when then aircraft comes to rest after landing." As such, even a certificated pilot may not count taxi time when taxiing without the intent to fly as PIC time, so it seems reasonable to assume that this does not count as acting as PIC.

Excellent find!

"Return to service" has nothing to do with taxiing. It is an airframe logbook entry, as per 43.9: "(4) If the work performed on the aircraft, airframe, aircraft engine, propeller, appliance, or component part has been performed satisfactorily, the signature, certificate number, and kind of certificate held by the person approving the work. The signature constitutes the approval for return to service only for the work performed."

Interesting, I was under the impression that return to service also included a test flight (and taxi by necessity)

91.407: http://www.ecfr.gov/cgi-bin/text-idx?node=14:2.0.1.3.10#se14.2.91_1407 "(b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records."

(con't) (a) No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless—
(1) It has been approved for return to service by a person authorized under §43.7 of this chapter; and
(2) The maintenance record entry required by §43.9 or §43.11, as applicable, of this chapter has been made.

return to service covers all maintenance, while not all maintenance requires a test flight.  and i've never seen a taxi test required of itself.

Yes, as per 61.113:

(a) Except as provided in paragraphs (b) through (h) of this section,
  no person who holds a private pilot certificate may act as pilot in
  command of an aircraft that is carrying passengers or property for
  compensation or hire; nor may that person, for compensation or hire,
  act as pilot in command of an aircraft.

A person taxiing an aircraft that is not intended for flight is not acting as PIC under this rule, and therefore can not only be a private pilot, but the person doesn't have to be a pilot at all.
There is no specific FAR that qualifies someone to taxi an aircraft, but aircraft operators and maintenance shops train and authorize mechanics to taxi and run-up engines.
Some individual airports have regulations that specify who may taxi and run-up an engine, such as Palm Springs:

(a)      Only qualified persons shall start and/or operate an Aircraft
  engine at the Airport and/or taxi an Aircraft on the Airport.
  Qualified persons include a pilot, an airframe and power plant
  mechanic, or a qualified technician licensed by the FAA and qualified
  to start or operate the engine(s) and/or taxi that particular type and
  class of Aircraft.

and Whitman County Airport:

14.20.130 - Who may taxi aircraft.  No person other than a mechanic, pilot, or properly authorized student pilot, certified by the FAA,
  shall taxi aircraft on any part of the airport.

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text:
Do I need to get a new AFSP approval if I change to a new part 61 instructor?
I have an AFSP (TSA) approval to train with a part 61 provider. I want to transfer from them to an individual part 61 CFI. Do I need to go through the AFSP approval process again?

Your question is a little unclear. Do you already have TSA approval to train at a part 141 school, but you want to switch to a part 61 instructor? If so, is your question whether that requires another TSA approval?

i have approval to train at part 61, and want to switch to part 61 instructor for a Private Pilot License.

Yes, you will need to apply for AFSP approval for your new training provider. The Application Guide for the AFSP says in step 7:

It is possible for a Candidate to have several active training requests at a given time. These requests may be for the same or different flight training providers. Each training request form will be processed separately; AFSP approval is valid only for the Provider listed in the application.

So if you needed AFSP approval for your original training provider, you will need a new approval to switch to a different provider.

Yes you do.  I've had two Germans and an Indian receive training from me while here on visas.  I was freelance, and they all had to go through ASFP.
There must be a new training request submitted each time a student in this situation changes training providers, and yes, I had to register with flightschoolcandidates.gov as a flight training provider and was involved with the students' application processes.

did you have to register with AFSP or TSA as a flight trainer so people could select your name as instructor. Because i see only flight schools in the list

The question was rewritten and now this does not answer it.

@Arun yes, you will need to communicate with your desired instructor on this issue.  He/she will need to register.

Yes, every flight school change is a new request according to the AOPA FAQ for aliens. You might not need to give fingerprints but you will have to pay the 130$ registration fee again to go to a different flight school.

You can't transfer an approval so yes, you need to get a new one. From AFSP's Application Guide:

TSA cannot transfer your training event request from one flight training provider to another flight training provider. TSA approval is
  valid only for the flight training provider listed on the training
  event request.
You may desire to build more flight hours than the flight training provider can accommodate. You may train simultaneously with more than
  one flight training provider; however, you must submit a flight
  training event request for each provider.

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text:
How many aluminum panels on the top of a 172M wing from 1972?
I'm looking into getting a wing to do some experiments prior to modifying an actual aircraft. Thanks to awesome folks on this forum, I've been able to find the wing of a 172M from 1972 that I can pick up now.
However, I still need to know approximately how many panels are on the top of this specific wing. For example, anything like this 172S or this 172P would be perfect for me, while this PA28-140 configuration wouldn't work (too many panels). Do you know how I could find out about those panels for the 172M from 1972?
Thanks!

What you are looking at on the top of the 172 wing is the rib rivets not individual panels. It should be a single sheet of aluminum riveted to the ribs, they are just in a rectangular pattern to match the underlying ribs and stringers. It may be one sheet for the top, and one for the leading edge...

Hi Ron, thanks for the info - if you're right this is amazing for me. Are you 100% sure for the 172M? I understand your point about the rivets vs. panels, I am just wondering because in the case of the PA28-140, there are actually quite a few distinct panels on the top of the wing. Just want to make sure it's not the case for the 172M before I rent a U-Haul truck!

I'm fairly certain, however the person you are getting the wing from should be able to provide you detailed photographs.

Thanks! I asked but the hangar is dark and the top of the wing leaning against the wall, and the person can't move it alone apparently.

You way want to take a look at this video of a 172 wing rebuild. The wing is not lots of tiny panels but what you are seeing is the areas that the rivets are placed to hold the larger panel on.

Amazing! This seems to indicate that the number of panels were already low in the 172 in 1957, good news for me and my 1972 wing...


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What should I know for my first aerobatic competition?
I'm flying my first aerobatic competition in a few weeks (in a Pitts S2A) and was wondering what I don't know about aerobatics? I have an infinite amount of learning to do - I have a basic knowledge of flying the figures, the "box", and a loose handle on reading Aresti. If anyone could give me an outline of the essential items to know before performing in my first (Club Known) competition I'd really appreciate it.
Equally, what is the step up like from Club to Sports sequences? The figures are a bit more complex, but is there more to think about than just this?
Many thanks from a newbie aerobatic pilot

Surely you have an instructor who recommended that you are ready to enter such a competition.

Stay alive and don’t do stupid thing without practice first. Good luck.

@Jim - yep just thought there'd be no harm in getting the internet's thoughts on it too

@Harry-Karmel, "no one ever got bad advice from the internetz", said no one, ever!

I strongly suggest that you read the accident report involving a Hunter aircraft that happened in the UK a few years ago (Shoreham).  It only took a few seconds for a relatively basic aerobatic maneuver to end in tears.  Plenty of lessons learned in that one for a new display pilot. Also consider this musing from an old display pilot

If this is an IAC contest, there will be a pilot's briefing before the contest begins.  One of the standard questions is "are there any first time competitors here?".  Raise your hand and you'll be assigned a "buddy" to walk you through the process.
It also doesn't hurt to contact the Contest Director a week or two ahead of the contest & have a conversation.
Remember that your priorities should be

Remain safe
Stay legal
Have fun
Fly well

in that order.  Remember that everyone's new at the beginning and minor mistakes are expected.


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How do you win a simulated dogfight/Air-to-Air engagement?
When simulating/practicing a dogfight/air-to-air engagement obviously real, live weapons aren't used. So therefore, how is it that these missions are "won"?
So my first question is: In a within visual range fight (assuming FOX 2/guns distances) how is the fight won? Is it determined by who can sit on the 6 o'clock of their opponent, or is there a system kind of like laser tag to determine if a gun shot (or missile simulation) lands on target.
And 2: How can you simulate/practice BVR engagements? Is there a way to effectively use a "virtual reality" missile that can simulate if the target is hit, and further to that, do Countermeasures have any relevance in these practice engagements?

I'd bet the winners of many of these engagements are decided at the bar later.

Bear in mind that most of my maneuvering was done from a defensive position due to the aircraft I flew, and that my experience spanned a period 15-30 years ago.  But, I have some perspective that may help answer the question.
First, as a comment mentioned, some are decided at the bar later.  (with hands shooting down watches…)  We also had a saying:  “First person to the chalkboard wins”.  This is in reference to the post-flight debrief practice of diagraming each engagement out on the board, and how whoever was doing the debrief may slant their interpretation of the fight to favor them.
The reality though is that despite egos and the competitive nature of practice fighting we never really tallied or recorded "wins" and losses.  The objective was always to learn, practice, and improve.  There is an honor system in place, and truthfulness is expected to prevail in the debrief.  Just like when wrestling or playing other games as a child, you pretty much know when you have been bested.  And if you try to BS or make excuses you will be called out and very quickly discredited.  So the short answer is that your guess that it is determined by who can sit at their opponent's 6 O’Clock isn’t all that far off.
To get more specific regarding the details of your question, it also depends on the equipment on the aircraft, as well as the level of training being conducted.  ACM (air combat maneuvering) can be as informal as a couple of squadron peers with no special gear scheduled for a local 1v1 proficiency flight, (and good naturedly arguing over who won later) or it could be a large scale coordinated exercise like Red Flag, or a Battlegroup at sea.
In the case of the former, BVR or even close in missile shots or guns would be called on the radio.  The target aircraft will usually respond “chaff/flares” and continue to maneuver.  If the shooter assesses a high probability of countermeasure success, they would respond “continue”.  A successful bug-out or assessed simulated kill by the flight lead would result in a “terminate” or “knock-it-off” call, followed by resetting to predetermined positions and altitude blocks for the next engagement.  Brief notes and fight diagrams will be drawn up on the pilot’s kneeboard during each reset to facilitate debriefing later.  Any disputes can likely be settled by reviewing the HUD video.
If the aircraft is equipped with a CATM (captive air training missile) and/or chaff and flares it will make the training that much more realistic.  The CATM will have all the electronics of a live missile, but no propellant or warhead.  This will allow the offensive fighter to obtain a missile lock, triggering the defender’s RWR, (radar warning receiver) and give the defender a chance to break the missile lock by dispensing actual countermeasures.  (and reinforce use of the correct button – because in a real fight you would want to pump out actual chaff/flares, not key the radio mic!)
In training there are often altitude restrictions on the use of flares, or they may be prohibited entirely depending on the fire danger in the training range area.
For large scale multi-aircraft exercises, the aircraft are usually fitted with an ACMI pod as described here:  https://en.wikipedia.org/wiki/Air_combat_maneuvering_instrumentation
Results are live streamed back to the exercise commanders and staff.  (Picture Flightaware combined with LiveATC, displayed on a wall sized screen, with a room full of professional pilots and controllers critiquing every move.)  These exercise monitors will act as referees in real time, and call out kills as they occur.  The “dead” aircraft will acknowledge, change their squawk to a prebriefed code so they can be identified by remaining participants, change altitude to a safe block, and transit to a designated area to hang out (in shame) until the end of the engagement.
The entire exercise is played back later on the big screen in a theater sized debrief room.  It can be sped up or slowed down as needed.  (As cheesy as the first TopGun movie is, you can see an example of the kind of displays that were in use at the time, and that as I remember were very similar to what was still being used in the early 2000s when I did my last Red Flag)
The debrief lead will provide commentary as it goes, and may pause to ask the pilots for their perspective.  For example:
Debriefer – “Hammer15, you were in missile range here when you called the ‘Fox2’, but based on the opening speed of Nail30 we assessed this as a successful bug-out, do you concur?”
Hammer15 – “Yes, I was showing ___ knots, and the CATM broke lock shortly after that…”

What does "hands shooting down watches" mean?

@user3067860 Imagine somebody describing an engagement using their hands to demonstrate positions of two aircraft -  most often an engagement they won, because who wants to talk about one they lost. You're probably going to use your primary hand for your own aircraft, and your off-hand for the opponent. Most people wear their watch on their off-hand, so it's your hand shooting down your watch.

Perhaps I could have described it better, but I was trying to convey the classic image of fighter pilots describing a dogfight using their hands.  To see an example, go here and scroll down to the photo of the Colonel in his uniform:  https://www.cbi-theater.com/life041243/life041243.html

Although my experience and knowledge in this field is from a computer science background and likely much less than other posters, I recently watched the Alpha Dogfight Trials, which I think you would find interesting as it is highly pertinent to your question. The basis on which an enemy simulated aircraft was determined to be shot down was based on the ability of a plane to keep a "firing cone" that protruded from the aircraft's main gun position and had a FOV of about 1.5 degrees.
I have no knowledge of how a BVR engagement would really be played out, so I will leave that part to others, but in regards to simulation the software and systems running on the missile/launch and control systems can be virtualized with their outputted telemetry and aerodynamic adjustment data fed into a simulated environment, and simulated data being fed to the sensors.


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Is there an upper age limit for pilots freight only?
When I asked my original question below, I should have been more specific. I will rephrase my question, however, I do wish to extend my thanks & appreciation to those who answered my question as previously written!
Please advise whether there is an upper age limit for pilots flying strictly air freight and/or for companies like FedEx, UPS, DHL, etc. that fly a mix of air freight, documentation, etc. flying on american (USA) flag carriers within the USA? and, whether it makes a difference if the same USA carrier flies out of the USA to another country such as Canada, Mexico, central America, south America, Europe, Asia, Africa, etc.? Does the US postal service its own fleet of aircraft, and, if so, does it have an upper age limit for flying US mail and/or parcels?
Prior question left here for reference only:
(Please advise if there is an upper age limit for pilots flying aircraft carrying only freight (not passengers) into and out of the USA?)

Part 121: yes.  Other parts: no.

In and out of USA? Does the plane registered in USA or you are a Mexican pilot fly into and out of USA?

All CAPS hurts my eyes!

The only situation in which a US-licensed pilot is subject to an age limit is part 121 scheduled airline service. Other than that there are no age limits, you just have to be able to pass your medical exam.
However, you state that in your scenario the pilot will have to be able to fly cargo in and out of the US. That implies the pilot may have a foreign license, in which case you must refer to that country's regulations.

Most scheduled US carriers operate under part 121, regardless of whether they carry passengers or cargo (or both), and part 121 has an age limit of 65.
Unscheduled US carriers (and very small scheduled ones) operate under part 135; neither has an age limit.
Either way, keeping a medical certificate can get very challenging with advanced age, as does continuing to pass flight reviews, so even where there is no official age limit, you won’t see many pilots over 60-65 anyway.
Under the Chicago Convention, US rules always apply to US crews on US planes, even if they happen to be in another country. So, FedEx and UPS can use 65yo pilots even when flying to/from/over countries that have a limit of 60 for their own pilots.
The US Postal Service has always used private airlines to move airmail. But if they instead had their own fleet, the answer would depend on whether the courts decided carrying mail was a “commercial purpose” or “governmental function”. If the former, they’d be “civil aircraft” and fall under Part 121, same as FedEx and UPS. If the latter, they’d be “public aircraft” (ICAO: “state aircraft”) and be exempt from part 121, including its age limit.

That last paragraph about "state aircraft" - can you give a reference, or an example of that?

I understand what the statement you made means, I'm looking for a cite to give it legitimacy, and/or an example of a non-military agency that owns aircraft and so does not follow FAA rules.

@DJClayworth Federal, state (in the US sense) and local law enforcement helicopters are common non-military examples. Most voluntarily follow FAA rules when they make sense (e.g. requiring pilots to have the relevant FAA license) but freely ignore them when they don’t (e.g. violating restricted airspace or refusing to yield to other aircraft while pursuing a suspect).

Again, a cite for this please?

@DJClayworth See 14 CFR 1.1 for the definitions of civil aircraft and public (ICAO: state) aircraft, and you can look through every other Part of 14 CFR to see that most rules only apply to “civil aircraft”.

Part 135 carriers can and do run scheduled operations.

@MichaelHall Fixed.

So, you're saying that while participating in a car chase, a police helicopter can violate Class B airspace, say LAX, disregarding ATC and all other rules, including over-flying the active runways, at need?

@CGCampbell 91.133(a), (c) and (d) apply to “an aircraft”, while 91.133(b) only applies to “a civil aircraft”. So, a police helicopter would need a clearance, radio, mode C and ADSB to operate in class B, but they wouldn’t need a pilot’s license.

@DJClayworth FAA Advisory Circular 00-1.1B gives an overview of public aircraft operations and the limits of FAA regulation. Also see this question.


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can one airplane be listed in the OPS Specs of 2 different airlines
Can an airplane be listed in the OPS Specs of 2 different airlines? One airline, Atlas also holds the Polar operating certificate.  They are two different operation certificates.  Can one airplane be listed in both Atlas and Polar ops specs?

Welcome to Av.SE!


text:
How do Private Helipads Work regarding Airspace?
For executive helipads or helipads run by a private company but not within airport airspace (tourism or shuttle helicopters for example), how do they work from a regulations standpoint?
Do pilots just contact the nearest Center frequency when taking off? Do they technically act as their own ATC or non-ATC traffic zones?

Just as a general note, the FAA does define a Helipad at 90' square clear of obstructions. You can land off airport anywhere you can safely get out of and have permission from the land owner, but that is the minimum size  for an official helipad.

To expand somewhat on HiddenWindshield's answer:
From an ATC perspective we don't know and don't care if an airport is publically (municipally) owned, or privately-owned but public-use, or privately-owned and restricted-use. The regulations for ATC don't take that into consideration. The pilots request to fly into a given airport and ATC provides the relevant and required spacing and sequencing services without investigating further; if it turns out that the pilot didn't have permission to use the airport that's between the pilot and the airport owner, and possibly the local Flight Standards District Office.
As far as airports are concerned, there are two major categories:

Towered.
Non-towered.

All towered airports will reside within some form of controlled-to-the-ground airspace (at least during the hours when the tower is open). This is airspace in which some form of air traffic control is available. In all types of controlled airspace, aircraft operating under Instrument Flight Rules (IFR) are provided separation between each other.1 Whether IFR aircraft are provided some type of airborne separation between them and aircraft operating under Visual Flight Rules (VFR), and whether two VFR aircraft are provided airborne separation between each other, depends on the specific class of controlled airspace.
Some non-towered airports exist in controlled airspace that extends to the ground, in order to provide better service to IFR aircraft operating there, or because they are very close to a towered airport. Many more non-towered airports exist in uncontrolled (Class G) airspace. Generally, all airspace up to at least 700' AGL (in most of the country 1200' AGL, and in certain isolated areas up to 14,500' MSL) is uncontrolled.
So as HiddenWindshield said, at many of those non-towered fields and helipads, there is no ATC service available, not even from Center (because the field exists in low-level uncontrolled airspace). Even at fields within controlled airspace, ATC will only
"clear" a helicopter for landing or takeoff if they are operating on the movement area (ATC-controlled region) of a towered airport. A helicopter operating at an off-airport helipad or even on a non-movement-area ramp at the airport will be told that landing or departure will be "at their own risk," meaning it is up to the pilot to check their surroundings and ensure the safety of the operation.

1Except in Class F airspace, which the US does not have but does exist in other countries.

In GA, and even more so with helicopters, it's perfectly possible to land in places that aren't airports at all, and which are in uncontrolled airspace.  And of course take off again: I'm not including emergency landings.

In the US if you have permission from the land owner you can land off airport at the property and it is treated like a non-tower airport. you should announce your intentions on the local CTAF frequency any time you are flying VFR and entering or exiting the airspace.

If an aircraft isn't flying in controlled airspace and is under Visual Flight Rules, then there's no requirement for the pilot to contact ATC at all. In fact, the plane doesn't even need to have a working radio onboard.
So, in that scenario, there is no ATC, and each pilot using the field just watches out for any other traffic.

On the other hand, there are good chances an "executive helipad" is within a busy controlled airspace, perhaps with a specific regulation.

@mins True, but the OP asked about helipads that are "not within airport aerospace", which I interpreted to mean "controlled airspace".

They function just like any other private airport.  If the heliport is towered, the tower would hand departing traffic over to the appropriate departure controllers depending on the nature of the flight and the helipad’s proximity to other controlled airspace (IFR and VFR ops).  If the helipad was non-towered, but lies within controlled airspace at the surface ie Class B, C, or D airspace, a helicopter pilot would contact the appropriate controller agency ASAP after departing (IFR and VFR ops).  If the helipad were non towered and in Class G surface airspace, you would contact the appropriate ARTCC controller before entering nearby controlled airspace (IFR).  If VFR no further action is required after departure.


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Why are hydraulic pumps mounted on engines 2 and 3 in BAe 146?
The BAe 146 has 4 engines:

engine no. 1 and 4 generate electricity
engine no. 2 and 3 generate hydraulic pressure

Why was this setup chosen?

Answer should be posted as answers, not as comments

I think you question may be too vague: BAe 146 has two electrical buses and two hydraulic systems, so I'm not surprised they've chosen two engines for the electrical and two for the hydraulics. Why they select that engines or why not having an extra generator/hydraulic pumps is a design choice difficult to say...


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For find a value of obstacles height below mentioned in intermediate segment why I should take the IAF MOCA instead of FAF MOCA?

It is said that we have to think all risk of flight in this segment that's why we have to take the 4420ft because the plane can be situated any point in this interval

I am not sure if I fully understand your question. This may be the answer. If the Intermediate Segment does not have a published MOCA altitude, and there is no crossing altitude for the Intermediate Fix, you should stay at or above the Initial Segment MOCA. You can only descend when you are given published or explicit ATC instructions to do so.


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With a Pandememic grounding many to their residence.... How to maintain flight hours?
No matter your Country, is grounding affecting license requirements(Passenger, Cargo or even Private) and how are the hours being rectified. CNN actually posed a great question in this article and I am also curious to know if this has been addressed CNN: What happens when pilots don't get their flying hours?.
https://www.cnn.com/travel/article/pilots-recency-flying-hours/index.html

Are you only interesting by FAA? Moreover, if your question is specific to the covid19 pandemic, you should precise it (each drop in airline traffic may have different causes -e.g. volcan ashes-, impact the industry differently -cf cargo flight vs passenger flights vs GA-  and thus each responses by EASA, FAA, ... are not the same)

I am trying to get at hrs req's for any Country or cargo to passenger really, this shutdown causes license issues and I am wondering how that is being considered.

You should edit the question to include your last comment. I'm not sure you are asking for any country. There are country with few international flight and/or no commercial flights (e.g. Eritrea, North Korea). On my side, I'm more worried for GA. You can also consider edit tags if you are interested by not only FAA regulations

Note that cargo are not as affected as passengers by grounding due to covid19. Almost all international flights are cargo (med supplies and other shipping).

Many countries are extending validation periods, but ultimately it's a question that isn't fully answered yet. Right now the focus is on the pandemic - the practical concequences come second.
Chances are it will be a combination of extending legally mandated periods, and common sense by operators.


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What are typical control surface deflections?
How can I tell what a reasonable control surface deflection is?
For example, is a 10 deg aileron deflection reasonable? Or a 0.5 degree aileron deflection? Is that too little? Too much? Same question concerning stab/rudder. I'm  not a pilot, I've never seen these surfaces actually in action, so it's kind of difficult to tell what (roughly) a reasonable surface deflection would be. As I go through flight data, I find myself seeing this type of data a lot, so an idea of what's reasonable would be really useful!

This question is extremely broad. A reasonable control surface deflection at one speed may tear the plane apart at a higher speed, as was the case with American Airlines 587. Likewise, this varies by plane; an Extra aerobatic plane might need to deflect surfaces by almost 70º which is not desirable on most other types of aircraft.

"I'm not a pilot"  So go search a local small airport and take a lesson or two.  Flying is a lot of fun.  I can't say how much deflection I use in normal turns, same as I couldn't say how much steering wheel turn correlates to how much the front wheels actually turn - you just steer until it's enough for where  you're trying to go.  Plane yoke controls turn a lot less than a car steering wheel - the amount of turn is more like a Formula 1 wheel's amount of turn, or even less.  I don't think the yoke on my Cessna turns as much as 90 degrees.

I'm curious as to exactly where you are encountering this data.  Accident reports?  Is that why you can't assume that actual data you are seeing is "reasonable"-- because they represent non-normal situations?

@quietflyer Yes, the plane was in an accident. It's unmanned. I'm going over some data for work, and as an inexperienced engineer, I really don't have much to go on.

Can you get some similar data from the same aircraft type from flights that were successful?  That seems to be what you need to do.

@quietflyer I've looked at some historical data, but my problem is more "how do I know that this value is legitimate?" Or, in other words, what if it was always wrong? I guess I might need to go back to when the system was initially verified and check the method by which is was verified. Thanks!

As others have noted, it is entirely relative and dependent on airspeed, phase of flight, and pilot intent.  It's like asking "what is a reasonable angular rotation of an automobile's steering wheel?"  The answer is vastly different if you are parallel parking vs staying in your lane on the freeway through a gentle curve.

If you have flight data (ie measured surface deflections), then wouldn't those be the final word?

Not really a control surface as such, but on light aircraft a $30^\circ$ flap angle is not uncommon.

The maximum useable deflection angle depends on the relative chord of the control surface. A good first-order value is ±20° for a 20% chord. With increasing chord, the deflection range will become smaller, like ±15° for a 30% flap.
With ailerons, things are a bit different because they are part of a lifting surface. This gives them some pre-loading so the negative range (trailing edge up) will become larger than the positive range (trailing edge down). This is also useful to reduce control forces (aileron differential) so the useable range will be +10°/-25° for a 20% chord aileron.

This is thinking a little "outside the box", but one thing you could do is use to the internet to locate some manuals for some ready-to-fly radio-controlled model airplanes such as those produced by HobbyZone, etc.  The manuals will typically list "low rates" and "high rates" for each surface.  The "low rates" have to provide the minimum control throw that the pilot would likely want to use in any flight mode, including high-speed flight.  The "high rates" have to provide the control throw that the pilot would likely want to use during the most extreme maneuvers.  The pilot can switch back and forth between these two different modes at will during flight.  Forget about any model airplane that is promoted as being capable of "3-D" flying, because during this style of extreme flying, extreme throws are used that would not be representative of anything used in full-scale aircraft.  Obviously, you will find that aircraft intended to fly very fast will generally employ much smaller control throws than aircraft intended to fly slowly, and aircraft intended for aerobatics will employ larger control throws than aircraft not so intended.
The point here is that because the pilot can switch back and forth between low rates and high rates at will, the "low rates" do not have to be configured to provided all the possible deflection that the pilot might ever need, and therefore might reasonably be assumed to be based on deflection that the pilot actually might regularly employ in ordinary non-aerobatic flight.
With this method, you'd have to measure the control surfaces to come up with an angular deflection in degrees, because the values provided in these manuals will typically be a linear measurement of how far the surface moves from the neutral (centered) position, when the control stick is fully deflected.
Anyway, you'll find a tremendous variation in the recommended control throws, depending on the type of aircraft and the way it is intended to be flown-- just as is the case with full-scale aircraft.
I suspect what would really better suit your needs would be some actual flight-test data from full-scale aircraft, but I can't tell you where to easily find that.
You also could consider playing around with a flight simulator such as can run on a personal computer.  Some of them can be configured to display control surface deflections.  Some also have modes where they will fly through maneuvers for you, as a lesson.

There is no concrete answer for this. It all depends on aircraft, airspeed, air density, attitude, configuration, wing loading, and weight. For example, a Piper Archer at cruise airspeed in straight, level, unaccelerated flight will have very little deflection necessary in flight controls to change or maintain attitude of flight.
As you transition to slow flight, the control surfaces will become progressively “mushy”. They will become less effective, requiring more deflection to change or maintain attitude.
One caveat is that at slower air speeds, less change in attitude is required to change, maintain direction of flight. Another caveat is that at lower aircraft weights, full deflection of control surfaces will result in structural damage at lower air speeds. But, that is a whole other discussion.


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Are airfoil profiles patented? If not, why?
For something that takes so much research and can effect performance drastically, there seems to be no patents on airfoils.
Too simple in appearance to patent? They appear simple at first but the performance characteristics behind them are quite complex.
I have found patents describing 3D objects such as turbofan blades using a combination of airfoils, twist and sweep combined. There seems to be nothing showing or describing a 2D profile of a wing unless it's flaps.

By "2D" do you mean flat wings consisting of one surface with no camber?

@nielsnielsen I’m assuming the OP means the airfoil profile. For instance the Clark Y versus an Eppler 387.

There certainly are airfoils that are patented. Here is an example. Here is another airfoil by the famous aerodynamicist Richard Whitcomb. I think it is tricky in practice to obtain a patent in that you need to define the airfoil in a way that isn't so narrow as to be useless for protection. Just claiming a series of coordinates would provide very little protection as someone could make minor changes to avoid infringement.

I think this begs the question: How much of a change to the coordinates would be required to not be in violation of the patent?

@RockPaperLz-MaskitorCasket Depends entirely on how the claims are worded. While searching I found several patents related to wind turbines but very few for aircraft.

Yes, this is part of the patent process (and enforcement) is still very much a mystery to me.  I have a hunch it comes down to "it's up to the courts" (which vary from country to country), but I really don't know.

@RockPaperLz-MaskitorCasket I moderate the Ask Patents SE site so you can always ask questions there.

Wonderful. Thanks. I have so many questions about patents that I often feel overwhelmed by the topic.

Patenting an airfoil would be difficult- the owner of the patent would need to show that they had invented something new that wasn’t obvious, and to enforce the patent they would have to prove that somebody else’s airfoil was identical and not an improvement on the original design.  Given the NACA system for describing airfoils it would be difficult to claim that an airfoil for which there was already a name was your own invention.

Related: Submarine propeller profiles are usually not patented, but are often closely guarded secrets.  They are such secrets that the props are often covered before subs are hoisted into dry docks.  Sometimes they are even covered before the sub comes to the surface at any port.

I don't disagree, but there is nothing in principle that keeps someone from patenting an improvement in an existing airfoil assuming the improvement is sufficiently novel and non-obvious.

There are good reasons for not filing a patent.  In particular, the patent must disclose the details of the invention, and so unless the inventor has the resources to enforce the patent they may well prefer to keep the details secret, or at least not readily available.

@Frog, which is why submarine propellers are never patented: patent enforcement against the Soviet Union would take far more resources than the US was willing to use.

To offer an interpretive clarification:  By definition 2D and 3D imply two-dimensional and three-dimensional fluid flow.  A 2D profile is, by definition, a wing section or airfoil.  There are many applications for 3D flow analysis and proprietary/patented design of wings and engine turbines.  For instance, understanding 3D flow would be necessary in computational fluid dynamics for innovative winglet design to lower the drag of a wing and thereby improve fuel economy, or in the specialized modification of fairings on a wing or along the fuselage to limit flow interference and thereby reduce aerodynamic drag.  By definition, flaps usually means a segment along the trailing edge of a wing that can be extended, and deflected downward, to increase lift.  For heavy aircraft, such flaps are slotted.  The design for improved lift typically involves, in addition to the use of slotted flaps, leading-edge slats (a drooping, forward extension of the leading edge of a wing) that opens a slot to improve airflow over the upper surface of the wing and augment the improved lift from slotted flaps.
And now onward to airfoils.  There are airfoils that have been patented.  Many of those airfoils are designed for specialized or specific applications be they wings, propellers, or turbine blades. Patented design usually means the designer developed and applied new and original special processes, innovative procedures, or applications in the design and development of their airfoil. By originality of process and design, these are considered unique and patentable. Examples have been offered elsewhere in the answer to this question.
However, airfoil design in general may not involve this type of innovative originality, even though the designer's resulting airfoil is, in itself, highly original.  The typical development of airfoils for low-speed applications uses mathematical constructs involving conformal mapping and applications in fluid mechanics.  The mathematical basis for these designs originated in the early 20th century.  Developments in the theory were advanced during the Second World War through a careful review of mathematical theory and verification by wind-tunnel testing.  This work was done by the National Advisory Committee for Aeronautics, the predecessor of NASA. A considerable amount of this work has been published and is electronically available.  Among special advances in pre-1950 airfoil design were the use of boundary-layer control to lower airfoil drag, development of advanced flap systems to improve lift, and the development of more efficient propellers.
After 1950, the specialized design of airfoils diverged.  High-speed flight and the development of heavier, jet-powered aircraft, had different requirements and resulted in different advances in airfoil design.  Many of these advances are considered proprietary and by their very nature, are obscure. In many cases, these proprietary features have been patented. This same element also persisted in the design of low-speed airfoils.  Although the features of a design were easily recognized, understood, and attributed to known theory, backing out or reversing the process to obtain the procedure followed in developing the design would be protracted and considered largely impractical.  Unless, of course, one had critical and key insights to the applied theory. Consequently, such designs have been considered the intellectual property of the designer.  For all practical intents and purposes, this has been considered as good as a patent.
So if the point of a patent is to protect one's intellectual property and hopefully make money in licensing the use of that property, why would a designer simply put all that hard work out to be used for free? Actually, a lot of the design work that is not patented was not developed for free.  Airfoils were specifically designed for specialized applications in aeronautics by companies providing research grants for the development of the airfoil.  A general requirement is the publication of the results of the research, even though the specific procedures used in the design are not disclosed.  Features that are disclosed are related to the profile itself, and its aerodynamic tests in a wind tunnel or on an actual aircraft. The resulting payment for the research, and goodwill brought to the designer through recognition of the work, is usually satisfactory.

Most airfoils are based on designs studied by the American National Advisory Committee on Aeronautics (NACA), which later became part of the National Aviation and Space Administration (NASA). The government has decided to make this data publicly available. Although Wikipedia has a wonderfully complex article on the subject, NASA.gov has much more, and much of it is readable by someone who lacks multiple PHDs.


text:
Why would a plane fly in circles for 6-7 hours and then land?
I've seen similar questions asked but when I look at the flight path this seems quite different:
https://www.flightradar24.com/data/aircraft/f-gjfa

I'm trying to figure out why that kind of plane would fly in circles for 6-7 hours and then land.

See also: https://aviation.stackexchange.com/questions/80395/what-is-this-plane-flying-in-overlapping-circles-pattern-doing

The aircraft F-GJFA is operated by Aero-Sotravia and is used (among other things) for live broadcasting of TV signals during sporting events:

5 dedicated planes are available, they have been specially modified to
accommodate live recording equipment. This fleet makes us as the
largest European operator with more than 95% of the annual volume of
aerial television relay.
We broadcast the best of sporting events (Tour De France and other
cycling races, many marathons including Paris, IRC and WRC car
rallies, cross-country skiing, etc.) as well as major current events
(presidential elections, Telethon, etc.).

(Aero-Sotravia - Television relay)
The flight you show was on 20 May, which coincides with the Giro d'Italia sector from Sierre to Cassano Magnago:

(modified from cyclingnews.com)

Giro riders are fast, but planes are faster, hence flying a helix along the stage.  Maybe they should fit out an AN-2 as a relay aircraft (though it might not have a high enough ceiling for the lines of sight).


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Why is the APU controller and ECB located aft without ventilation on Boeing and Airbus aircraft?
On Boeing and Airbus aircraft, the APU controller and electronic control box (ECB) is located aft. Why is it located here, where no ventilation is available?
Why it is isolated from different line-replaceable units (LRUs)?

There are various inlets for APU. Google "APU inlets" with a specific aircraft type, and you get pictures (and location). APU is used a lot on ground, so you want to place where it will not interfere with ground handling. I think Centre-Of-Mass may be also relevant (on empty aircraft).

@GiacomoCatenazzi: can you post it as an answer? I think it's worth some upvotes

The question is asking why the electronic controller for the APU is located aft; the comment by @GiacomoCatenazzi talks about why the APU itself is located aft.  I don't think that would be an answer to the stated question.


text:
Nose wheels with camber
What is the reason for the inward slanting nose wheels on a Lockheed Constellation? Are there other aircraft with same design.

I believe this question is about the camber and it has already been asked. https://aviation.stackexchange.com/questions/65376/why-are-the-constellations-nosewheels-canted-inwards

The Connie's nose gear has the wheel axle almost on the same plane as the strut axis, so much of the castering effect is from the rake angle of the strut (like a motorcycle front fork - it's the rake angle of the fork, the slant, that makes the wheel want to caster).

This works best if the wheel pair's footprint is as narrow as possible, because when the wheel assembly with dual tires turns, the rake angle means one wheel wants to lift off the pavement a little bit (to visualize the effect, mentally take the rake angle all the way to 90 degrees and rotate the strut; one wheel lifts off the ground - go back up to 10 degrees like the Connie's nose strut; that effect, but much smaller).
Angling the wheels to get them close together at the bottom gets the narrowest possible footprint and minimizes the differential contact pressure of the tires as they rotate away from straight ahead, on a strut that is raked like that.

On most airliner nose gears with dual wheels, the strut is nearly vertical, so the steering axis is vertical, with all caster effect coming from the offset between the wheel axis and the steering axis, like a shopping cart caster. In that case the lateral wheel spacing isn't critical because the contact pressure of both tires is the same at all steering angles.

Maybe you can add this picture to show what you mean.

@sophit perfect thanks!

You're welcome. Don't forget the sources of the pictures.


text:
How to calculate the climb performance of an A320
Recently I have been taking off in Innsbruck (LOWI) with my A320 (in Microsoft Flight Simulator, because I cannot afford the real one) and quickly found myself greeted by a GPWS Warning: "Terrain ahead!". I have been flying the MOGTI 3H SID from Runway 26. The charts state a required minimum climb gradient of 11.0% (that is 2233 ft/min at 200 kts). I probably should have calculated the climb performance before taking off, but I don't know how to do that.
Are there any tables on the climb performance of an A320 with a given weight, flaps and slats config, engines etc.? I didn't find anything specific on the internet. Or is there a way to make the MCDU show me that?

Not quite what you are looking for but for sim purposes it might do. https://contentzone.eurocontrol.int/aircraftperformance/details.aspx?ICAO=A320

Most airlines have the NavBlue FlySmart software on a pilot tablet to calculate performance.
A rough way to calculate this is to use the MCDU. Convert your ft/min climb requirement to ft/nm.
$$ \frac{200 \, \text{kt}}{60 \, \text{min/h}} \approx 3.33 \, \text{NM/min} $$
$$ \frac{2233 \, \text{ft/min}}{3.33 \, \text{NM/min}} \approx 670 \, \text{ft/NM}$$
Check you first calculated waypoint crossing altitude on you MCDU to see if you comply.


text:
Does optimum IAS for climb vary with altitude?
I was in an argument about aerodynamics and we eventually derived an equation as follows.
So I'm going by this equation:
$$RoC = \frac{\eta_p P-VD}{W}$$
Where $\eta$ represents propeller efficiency.
Assuming low Mach number:
$$TAS = IAS \cdot \sqrt{\frac{\rho_0}{\rho}}$$
$$ \text{Drag} = k(TAS)^2 \rho = k(IAS)^2 \rho_0$$
$$ \text{Specific Power} := P_s = \frac{\eta_p P}{W}$$
$$ \text{Drag Power} := P_d = \frac{TAS \cdot D}{W} = k \frac{\rho (TAS)^3}{W} = k \rho_0 \sqrt{\frac{\rho_0}{\rho}} \frac{(IAS)^3}{W}$$
The optimum climb IAS is given by:
$$\frac{dP_s}{d(IAS)}= \frac{dP_d}{d(IAS)}$$
Without loss of generality:
$$\frac{d\eta_p}{d(IAS)} = k \frac{(IAS)^2}{\sqrt{\rho}}$$
So does optimum IAS for climb vary with altitude?

Your equations aren't quite right. For example, you use IAS where CAS is intended. And drag power is V D, not V D / W. (Energy is force times distance and power is force times velocity.) Additionally, prop efficiency is more a function of true airspeed and RPM, so to take the derivative relative to IAS won't give you a good read on the effects of altitude.
Essentially this question is a complicated balance of several relationships. CAS vs TAS with airspeed, CL/CD curve, power available (are you normally aspirated, turbocharged, turboprop, electric?), prop efficiency, and even engine cooling. (Certification requirements require adequate cooling at Vy and if cooling is inadequate, one trick is to in rease Vy.) And with higher HP to weight, pitch angle becomes a factor as some thrust is providing lift.
A better approach, in my opinion, is to look at a couple flight manuals. What you'll generally find is that Vy decreases a little with altitude - maybe a knot every 2,000 ft or so.


text:
Why does the pilot need to manually retard the thrust levers in an A320?
The Airbus A320 FCOM (Autoflight - Flight Guidance - Flare Mode) says:

At 30 ft RA, the AP/FD aligns the yaw axis with the runway centerline and the aircraft flares
on the pitch axis. If the autothrust is active, thrust is automatically reduced to IDLE.

So why do I need to retard the autothrust in manual landing?
I saw some captains retard in autoland at 10 ft?

So you are asking why you have to do something manually when you are in manual mode, when it does it automatically in automatic mode?  (By the definition of the terms  the question should be self answering...)  Am I missing some nuance here?

Dear Michael you remind me the joke " Oh look its flying by wire".Airbus and manual mode :)NOP

On Airbus aircraft¹, the "RETARD" callout occurs just before touchdown and acts as a reminder² for the pilot to put the thrust levers to idle. Regardless of whether the AP/AT is engaged or not - regardless of whether the thrust levers have already been "retarded" or not, this callout will reiterate from the time it starts until main-gear touchdown³.
If the A/Thr is engaged (like during autoland), it will automatically command idle power at the appropriate time during flare, but it is still necessary to manually retard the thrust levers to idle in order to be able to engage reverse thrust after touchdown⁴.

¹All Airbuses other than A-300, A-310 and A-220.
²This is a reminder - this is not a command. Ultimately, the pilot must decide exactly when it would be appropriate to retard the thrust levers based on the situation.
³Sometimes this callout will begin, but then shortly will be replaced with radio altimeter callouts.
⁴And even if reverse thrust need not be used, retarding the thrust levers is still necessary for the automatic deployment of ground spoilers and for autobrake activation.


text:
Why does adding more blades to a propeller/fan not show a decrease in efficiency?
According to this answer increasing blade solidity increases the blade area by either enlarging chord or increasing blade count both of which reduce efficiency via reducing the lift coefficient and increasing friction.
However, in fan maps of turbofans the efficiency of the fan is as high as 90%.
The word efficiency seems overloaded, meaning different things in the case of lightly loaded propellers compared to highly loaded fans.
What exactly are we measuring the efficiency of then?
If it's just measuring the efficiency of compression, how can we relate the "efficiency" of highly loaded fans to that of lightly loaded propellers?

Well, if you want to compare, you'll need the fan map of an engine with a high solidity and a different one with a low solidity.  You can't make any conclusion based on just one number.  That's like saying "I heard 8 cylinder engine car engines weigh more than 6 cylinder car engines, but here's a 8 cylinder engine that only weighs 450 pounds, and that seems small to me, so therefore 6 and 8 cylinder engines weigh the same".

@DanielK That wasn't what I was going for, I improved the question. Thanks.

Well, to me, the question is even less clear now.  I would suggest you start a new question, delete everything referring to the linked answer about solidity, and just ask a new question of "How is efficiency defined for a fan map for a turbofan", and then a second question "how is efficiency defined for a propeller".  I think that gets at what you are really trying to ask.


text:
Would air having an infinite speed of sound be ideal?
Hypothetically, if aerodynamicists had the opportunity to somehow raise the speed of sound in air to an infinite level so that air was no longer compressed, how would this affect aircraft related aerodynamics? Are there cases a higher speed of sound would be helpful rather than a hindrance?
Would subsonic aircraft designs be able to fly much faster without design changes?
Would we be able to design axial compressors with much higher pressure ratios per stage?
Perhaps much higher thrust could be generated from the same size propeller?
Are there cases where this would not be desirable? Such as spacecraft re-entry for instance?

I don't think they reference a Mach speed in outer space.

To "somehow raise the speed of sound in air to an infinite level so that air was no longer compressible" sounds more like WorldBuilding than Aviation to me.

@RalphJ You’re right, however I feel asking what if questions can increase our understanding. It is taken for granted that air compresses, what if it wasn’t compressible?  Would this be a much better world for the aerodynamicist?

@usernamechecksout wouldn't that be water?

@AadirajAnil Water is compressible, just less so. Generally the less compressible the medium the less time it takes for “information” to pass through it.

If air was not compressible, nothing could move at all.  Solids are not compressible, and we can't move through them.

@wbeard52 Air does not need to compress to allow objects to move through it. Air allows objects to pass since it is a gas with no inherent molecular structure and therefore no "resistance".

@usernamechecksout  I think you missed the point.  If air cannot be compressed any further, it becomes a solid and nothing can get through it.  If there was a path for any object to go through the super compressed air, by definition, the air can be compacted / compressed more.

@wbeard52 I changed the sentence from "so that air was no longer compressible" to "so that air was no longer compressed". Does this change your argument? In other words, if the speed of sound was raised high enough (through hypothetical means of course), air would no longer be compressed when being decelerated.

I think there's some misconception, and I hope you correct me if I'm wrong, the title is "infinite Mach", but you're saying you want to raise speed of sound to infinity, this means mach no. is zero, because $M = \frac{v}{a}$.
But why do you think decreasing compressibility is useful in aviation?
However, if I understood your question then the answer is: no, subsonic airplanes won't fly much faster if speed of sound $a=\infty$, actually they won't be able to fly at all. As people reffered out in the comments, a matter with infinite speed of sound is more likely to be a solid rather than a fluid. Of course, solids don't have infinite speeds of sound, but they're considered to be so in the context of studying fluid mechanics, because comparatively, speeds of sound in solids is much much higher than in any normal fluid.
Another way to think about it is: assuming $a=\infty$ might be somehow similar to assuming the velocity of the airplane is zero $v=0$, because both assumptions lead to zero mach no. $M = 0$ which means there's no motion of the body inside the domain that was once considered as a fluid.

Thank you for your answer. I realize that my title was asking the wrong question. I do mean an infinite speed of sound, not Mach number. I disagree that Mach=0 means no motion of the body. A Mach of 0 would mean there are no compressibility effects, not 0 motion. Mach isn't a measure of velocity.

Welcome to Aviation SE!  This answer's good enough to be your hundredth, not your first :-)

@usernamechecksout I agree that mach number is by definition: a measure of compressibility, but may be there's something I don't understand, why does a higher speed of sound mean higher velocity?
What I know is: I can only play with two things (independent variables in our context): velocity and speed of sound, so if I change the speed of sound of a fluid, this means that mach no. (dependent variable) changed, but it doesn't mean that velocity of airplane changed at all, because it's still independent of speed of sound.
Again, correct me if I'm wrong

@CamilleGoudeseune you're too generous sir, thank you a lot

@أحمدصلاح A higher speed of sound wouldn't change velocity. It only changes the ratio of velocity to the speed of sound. The lower the ratio the lower the Mach number, or in other words the compressibility. V could be any value you choose. If you're solving for V of course it wouldn't make sense for Mach to be 0 otherwise infinity*0=undefined velocity. Suggesting the use of infinity may have been a mistake on my part. I really meant "infinite" in more of the common english definition not the mathematical one. I am learning all of this as we go so correct me if I'm wrong.

@CamilleGoudeseune Ok so I agree that increasing speed of sound means decreasing mach no. this is totally right, despite of the velocity still what I don't understand is: why is decreasing mach no. useful anyway, why is a less compressible air better for the airplane?

Less compressibility improves flight for the reasons listed in sophit's answer's last paragraph.  I couldn't say it better than that.

Hypothetically, if aerodynamicists had the opportunity to somehow raise the speed of sound in air to an infinite level so that air was no longer compressed, how would this affect aircraft related aerodynamics?

The aerodynamics would just look like incompressible aerodynamics i.e. just like any aerodynamics happening at Mach numbers smaller than 0.3. There wouldn't be any difference in respect to what it is already known about that particular branch of aerodynamics.
If you want to keep the fluid incompressible (Mach number <0.3) but travel anyway faster, you just have to increase the speed of sound either by playing around with the fluid and/or its temperature: this is something normally achieved in "cryogenic wind tunnels".
Obviously getting rid of all the side effects of compressibility (wave drag, shift of the aerodynamic centre, shockwaves,... ) would have, in general, a net positive effect, mainly less drag.


text:
Vertical autorotation with passive rotor
Let's say we have a simple hollow cube(chosen for simplicity) with outside side length=10cm, thickness=5mm (or another arbitrary shape with arbitrary dimensions).
Clarification: I am NOT talking about a helicopter. It has no tail rotor, no forward speed, no controllers etc.
It has a passive rotor(no power, no engine) on top of it with 4 blades(total diameter of rotor l=30cm) (with arbitrary foil shape). We drop it from height of H.
What would be free-body diagram on this rotor-cube system?
I am imagining that there would be 3 forces. First one is downward and the other two is upward. Both velocities are descent velocities, the area S in both of them is $\frac{\pi l^2}{4}$, l being diameter of circle created by rotating blades.

Weight Force $W=mg$
Lift force $L=½ρv²SC_l$
Drag force $F_d=½ρv²SC_d$

Is this correct?  Also please post your source, whether the name of the book from or site link which you learned how to find free-body diagram of these kinds of aviation systems.
Also will all kinds of foils work in this scenario? What is the important parameter in foils that will make it start spinning and descent with constant speed?

There's some info on autorotation, including some references, in this answer. And also a pertinent question on Physics SE. Free body diagrams included.
In short:

Autorotation only works in a satisfactory way if the vehicle has forward velocity: in a vertical descent, in optimal circumstances, autorotation works as well as a leaky parachute does.
Getting the rotor to actually rotate from standstill is a hair raising kettle of fish, the first thing about autorotation that helicopter pilots learn is that they must maintain rotor rotation from when it was driven by an engine. During any time of rotor standstill the aircraft is simply falling, with no real means of aligning the rotor with the airflow.
Autogyro's start their flight by starting the rotor to rotate. Can be done on ground by driving fast and making use of the horizontal velocity, or by a flywheel mechanism attached to the propeller engine. Again, the first thing to do is to rotate the rotor.

The equations in OP are valid for fixed wing aeroplanes, and for the rotor blades. But since with rotor blades the velocity over the blade is a function of the blade radius, plus faster over the forward moving blade than over the retreating blade, they are not defined relative to airspeed V but to tip speed of the rotor blades $\Omega R$. Impulse theory using non dimensional coefficients, from Prouty Helicopter Performance, Stability and Control page 25:
$$ T = C_T \cdot \rho A (\Omega R)^2$$
with

T = rotor thrust
$\rho$ = air density
A = disk area
$\Omega R$ = tip speed

Note that Prouty uses the USA definition for $C_T$, which incorporates the factor ½ of the dynamic pressure $½ \rho V^2$ and is therefore twice as much as $C_T$ values used in Europe.
For the thrust to drive the rotor, analogous to aeroplane drag:
$$Q = C_Q \cdot \rho A (\Omega R)^2 R$$
And for the power:
$$P = C_P \cdot \rho A (\Omega R)^3$$

Also will all kinds of foils work in this scenario? What is the important parameter in foils that will make it start spinning and descent with constant speed?

Airfoil shape is of much less importance than blade twist, solidity ratio and a whole lot more parameters, which would make the answer very broad. Best looked up in Prouty and Leishman.

"Getting the rotor to actually rotate from standstill is a hair raising kettle of fish" - Can't we think of it as a wind turbine? Wind turbines are standing still until air is flowing through them, so can't it also work for a rotor?

Still-air vertical descents are quite feasible if you design the gear to handle the vertical velocity of around 500 fpm https://www.youtube.com/watch?v=GlyR-aSEuig.

Vertical descents are fine, the hard bit is stopping at the ground, as you only have stored energy in the blades. If you have some forward speed, you can use that energy too, and there's usually quite a lot of it, as forward speed is greater than vertical speed.

@photinaomo - helicopters typically only have a few degrees of negative pitch, so if they stop, they're deeply stalled and there's not much force turning them. Wind turbines can usually feather their blades to face the on-coming air. A typical paper helicopter starts from stationary, but drops rapidly for several feet while it does.

@RobinBennett  Autorotation pitch is, for the Reynolds numbers typical of helicopter blades & airspeeds, positive... About +3º...

What is the important parameter in foils that will make it start spinning

The aerofoil needs to create lift in a direction that causes rotation. Typically aerofoils stall at around 15 degrees angle of attack, so you would need to rotate your blades to around -75 degrees to get them started, and gradually reduce this as they speed up.

and descent with constant speed?

During descent, the blades have slight negative pitch, so their lift is tilted slightly in the direction of rotation, and provides the energy input to overcome drag. The angle of attack is still positive, as the aircraft is descending. If the blade speed and angle of attack are the same as for normal flight, so is the lift, and there is no vertical acceleration (i.e. you have constant speed descent).